On regular singleplayer I use function like this to check if player is holding down control key.

@OnlyIn(Dist.CLIENT)
public static boolean isHoldingControl() {
	return InputConstants.isKeyDown(Minecraft.getInstance().getWindow().getWindow(), GLFW.GLFW_KEY_LEFT_CONTROL) || 
		InputConstants.isKeyDown(Minecraft.getInstance().getWindow().getWindow(), GLFW.GLFW_KEY_RIGHT_CONTROL);
}

However, on multiplayer it throws an error, because this is a client-side function and the Minecraft class is also client-side (if I understand correctly). How can I make a function that would work for DEDICATED_SERVER as well? I guess I have to pass in a player as an argument, but I can't figure out how to check weather control is held or not. Thanks. 

Edited March 2, 20232 yr by RInventor7

You should use a KeyMapping for that, then check in ClientTickEvent KeyMapping#isDown and send the state of the KeyMapping via a custom network packet to the server.

To avoid sending a Packet each tick, you should send the Packet only if the KeyMapping got pressed or released (the state changed).